Complete Determination of Bulk Density and Coating Porosity, 2007 Coating & Graphic Arts Conference

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During mercury intrusion at low pressure into uncoated and pigment coated papers irreproducible large pore volumes are frequently recorded, which prevent detailed determination of total composite porosity by mercury porosimetry alone. An ovel occlusion correction procedure is reported here, in which the absorption volume of hexadecane into the void structures and its displacement by the skeletal structures are combined with the mercury intrusion data to allow the coating and the substrate to be separately assessed. This may be achieved by scaling the intrusion into the uncoated permeable substrate to that of the coated substrate intrusion curve. The resulting intrusion curve is then further scaled to an absolute porosity and bulk volume of the coated sample. The values so derived are compared to those obtained by the traditional method of approximating the intrusion volume into the coating, and comparing this with the same coating applied to an aluminium foil substrate. A method for estimating coating coverage derived from these analyses, by considering the modification of the base paper after coating in the region of the base coating interface pores, is described.